Electrical heating systems may be utilized to supplement the heat provided by an engine and to heat the passenger compartment of a vehicle. While often used in electric vehicles powered solely by a traction battery and hybrid electric vehicles having an internal combustion engine in combination with a fraction battery, such heating systems may also be found in other applications. For example, electric heating systems may be utilized in air conditioners, dehumidifiers, dryers, portable heaters and other electrical appliances.
To provide passenger comfort in vehicle applications, vehicles have the capability to heat or cool the passenger compartment. Conventional vehicles use waste heat from the engine as the sole source of heating for the passenger compartment. With the advent of Battery Electric Vehicles (BEV), there is little or no waste heat available for use in heating the vehicle cabin. As such, BEVs may use an electric heater to warm the passenger compartment. Similarly, although Hybrid Electric Vehicles (HEV) include a small internal combustion engine that may provide some waste heat for heating the vehicle cabin, these vehicles are designed to minimize the use of the engine to maximize fuel economy. As such, these vehicles pose different heating challenges because the engine may not always be running and generating waste heat for use by the heating system. Plug-in Hybrid Electric Vehicles (PHEV) compound this issue by running with the engine off for significant periods of time. To provide optimal fuel economy benefits, it is desired to heat the passenger compartment without having to rely solely on engine waste heat.
As such, various alternatives have been developed to heat the passenger compartment of electric and hybrid electric vehicles. One such solution uses an electric heater as a heat source to provide heat for electric vehicles or supplement heat from the engine in hybrid vehicles when engine waste heat is insufficient to meet a heating demand for the vehicle cabin. An electric heater generally contains one or more heating elements that function as electrical resistors that convert electricity to heat. Electric heaters may include a thermostat to regulate the heat output. Alternatively, electric heaters may include Positive Temperature Coefficient (PTC) heating elements. PTC heating elements are made of small ceramic stones that have an increasing electrical resistance as temperature increases to provide self-limiting temperature properties such that a thermostat is not required. In addition, PTC heaters have fast heating response times and the ability to automatically vary resistance and associated current/power to maintain a pre-defined temperature.
Various commercially available component electric heaters may include some integrated diagnostic or self-test functions to determine heater operating state. However, these diagnostics may not be sufficient or suitable for some applications. In particular, integrated heater diagnostics may not provide sufficient or timely feedback to determine whether the heater is functioning as desired for a particular application. In vehicle applications, these diagnostics may take several key cycles to detect or report various operating conditions, may be unable to detect some operating anomalies, and/or may not have desired accuracy or granularity in detecting various conditions.